In general, among methods for controlling traffic in a computer network, a control method for leveling traffic so as not to exceed the regulated maximum speed by adjusting the intervals of sending packets is referred to as traffic shaping. As traffic shaping control, a method for controlling the maximum transfer rate (rate is limited) is widely applied.
The traffic shaping is implemented mainly by hardware. In the traffic shaping, the traffic flow rate is measured by, in general, the token bucket algorithm, and each packet is buffered into each FIFO (First In First Out) buffer formed into a hierarchy and is output after being subjected to leveling and flow rate limitation so as to meet each traffic service level agreement (SLA).
In the above-mentioned hardware, there exists granularity which is feasible precision, for the setting of data rate desired to be limited, because of the token size of the token bucket algorithm and the transfer time difference of a packet having a variable length. At present, the physical interface of 10 Gbps has spread and 1 Mbps, 500 kbps, etc., are used generally as granularity thereof.
It should be noted that conventionally, there is proposed a packet communication system capable of realizing a system excellent in fairness of throughput between flows without causing deterioration of switch characteristics (for example, see Japanese Laid-Open Patent Publication No. 2003-143217).
Furthermore, there is proposed a packet relay capable of controlling the overall band of packets to be transmitted to a plurality of output lines (for example, see Japanese Laid-Open Patent Publication No. 2007-201965).
However, there has been a problem in which the shaper setting rate of traffic shaping does not agree with the band of the physical line of the output destination because of the presence of granularity at which a packet is shaped.
For example, the granularity of a shaping circuit for shaping a packet is set to 500 kbps, the shaper setting rate of the shaping circuit (band of the packet output from the shaping circuit) is set to 2.0 Mbps, and the band of the physical line of the output destination of the shaping circuit is set to 1.980 Mbps.
In this case, the output band of the shaping circuit becomes 20 kbps (2.0 Mbps-1.980 Mbps) surplus to the band of the physical line. Because of that, the surplus packets are disposed of before being output to the physical line.
Furthermore, in the above-mentioned conditions, it is assumed that the shaper setting rate of the shaping circuit is set to 1.5 Mbps.
In this case, the output band of the shaping circuit becomes short of 480 kbps (1.5 Mbps-1.980 Mbps) as compared with the band of the physical line. Because of that, the physical line does not use the full band corresponding thereto.